A JPEG fresh from a camera or design tool is often 4-8 MB. The same image at quality 85 is typically under 500 KB with no visible difference on a monitor. Understanding how compression works tells you exactly where that cutoff is — and where artifacts start appearing.
How JPEG compression actually works
JPEG uses a mathematical technique called DCT — discrete cosine transform. It breaks the image into 8×8 pixel blocks and represents each block as a combination of frequency patterns. High-quality settings keep more of those frequency patterns; lower quality settings discard the subtle ones.
The result of throwing away frequency data is visible as blockiness — squares appearing in areas of flat color like blue skies or solid walls. Artifacts are least visible in detailed, textured areas (foliage, fabric, faces) and most visible in smooth gradients and hard edges. This is why compression artifacts are easy to miss in typical photos but obvious in screenshots or graphics with text.
What quality setting to use
Quality 80-85 is visually indistinguishable from quality 100 on a standard screen. This is the range used by most professional image workflows and social platforms. Google's web.dev guidelines recommend quality 85 as a starting point for web images.
Quality 60-70 is perceptible on close inspection, particularly in smooth areas, but acceptable for thumbnails and non-critical images where file size is the priority. Below quality 60, blockiness becomes obvious even at normal viewing distance. Quality 90+ is appropriate when you plan to edit and re-save the file — each re-compression degrades the image, so starting higher gives you headroom.
Target file sizes by use case
For web hero images (full-width banners, feature images): aim for 80-150 KB. Images above 200 KB slow page load noticeably on mobile connections. For blog post body images: 40-80 KB. For email: stay under 100 KB — many email clients don't load images over that threshold automatically, and download cost matters on mobile.
For print: file size is less important than resolution. Print requires 300 DPI at the physical print size, and quality 90+ to avoid artifacts that become visible when enlarged. Web-optimized JPEGs at 72-96 DPI will print poorly — don't use a compressed web file for print without checking the actual pixel dimensions first.
How to compress a JPEG online
Go to the image compressor. Upload your JPG file. The tool shows you the original file size and lets you choose a quality level or a target file size. Adjust the quality slider — the preview updates to show the output size estimate.
Download the compressed file. If you need further control over dimensions or format, the image optimizer lets you resize and compress in one step. For batch compression of multiple files, upload them together and download the ZIP.
When WebP is a better choice than JPEG
If the image is going on a website and all your target browsers support WebP (every major browser has since 2020), WebP at equivalent quality is 25-34% smaller than JPEG. For transparency, WebP is the only choice — JPEG can't store an alpha channel.
JPEG is still the right format for email attachments, stock photo submissions, and any context where WebP compatibility isn't guaranteed. The JPG to WebP converter handles the switch when you're ready for it.
The compression setting that works
Quality 85 is the practical default for most JPEG compression. It produces files 60-70% smaller than quality 100 with no visible degradation on screen. Drop to quality 75-80 if you need to hit a specific file size target. Stay at 90+ if the file will be edited again. Those three rules cover 95% of real-world use cases.